PROJECT SUMMARY This project aims to define how polymicrobial infection influences bacterial otitis media. Haemophilus influenzae (Hi), Streptococcus pneumoniae (Sp), and Moraxella catarrhalis (Mcat) are the predominant isolates from patients with OM, and a wealth of evidence indicates that OM often involves combinations of these organisms. We hypothesize that interactions between bacterial species can impact OM disease parameters that include bacterial persistence, resistance to clearance and antibiotic treatment, and the initiation, progression and severity of the host inflammatory response. In order to address this hypothesis we will complete the following Specific Aims: Specific Aim 1: To define interactions among bacterial pathogens causing OM. Specific Aim 2. To ask how different interspecies relationships affect experimental OM. Specific Aim 3. To evaluate impact of polymicrobial infection on antibiotic resistance. Specific Aim 4. To establish the incidence of coinfection in patients undergoing tympanostomy. Most of our current knowledge about bacterial pathogenesis is derived from infection studies using pure cultures that may not fully represent how infections occur in actual patients. This proposal presents an opportunity to learn how multiple pathogens inhabiting the same ecological niche influence one another in biofilm communities that are critical to persistent infections.